This invention relates to sequential flotation of sulfide ores and, more particularly, to the sequential and selective initial flotation of the copper component directly from ores containing copper sulfide and the sulfide of other metals such as lead and zinc.
Copper-lead and copper-lead-zinc ores of the type common to the lead belt areas of southeastern Missouri are complex ores and contain galena, sphalerite, pyrite and copper sulfides such as chalcopyrite or chalcocite in a siliceous carbonate matrix. The usual methods for treatment of copper-lead-zinc sulfide ores include the selective depression of zinc with cyanide and/or zinc sulfate, or a sulfite, followed by the selection flotation of a bulk copper-lead concentrate using xanthates, mercaptobenzothiazole or diaryl dithiophosphate collectors with known frothers. The zinc minerals remaining in the copper-lead tailings are then conditioned with a soluble copper solution, usually copper sulfate with lime added for pH control, and are floated with a zinc collector. The bulk copper-lead concentrate is further treated to separate the lead and copper sulfides.
One method for treating bulk copper-lead concentrates having a lead-copper ratio of about 5 to 1 involves contacting the concentrates with 1.5 to 2.0 lb./ton SO.sub.2 in a tower with the discharge from the tower being conditioned for 20 minutes with 3 to 5 lb./ton sodium dichromate to depress lead. The pH is adjusted to about 5 with lime for copper flotation and selectivity is achieved through four to five cleaning stages in which cyanide is used. A second method is used in making a separation of copper and lead from bulk concentrates in which the lead to copper ratio is less than 2 to 1 with the copper mineral being a coarse, unaltered chalcopyrite. In this method, the separation is made with either straight cyanide or with a zinc-cyanide compound as a copper depressant. If straight cyanide is used, considerable loss of copper and gold values occurs through dissolution, but these losses are eliminated when the zinc-cyanide complex is used. In a third method employed for bulk copper-lead concentrates having a high lead to copper ratio, the concentrate is treated with sulphurous acid and boiled starch to depress lead and the pH is held at 6. Starch is also used in the roughers and cleaners. Alternatively, in this method, the bulk copper-lead concentrate is passed through an SO.sub.2 tower with reagent consumption being about 4 lb./ton sulfur and 0.6 lb./ton corn starch.
In addition, one method is known for making a direct separation of copper, lead and zinc in the rougher flotation circuit from an ore consisting of sphalerite, galena, pyrite and chalcopyrite. In this method, copper is floated first after SO.sub.2 has been added in the grinding circuit to depress zinc. Lead is next recovered with cyanide being added to depress zinc.
U.S. patents concerned with recovery of copper from complex ores by flotation include U.S. Pat. Nos. 3,220,551; 4,283,017 and 4,460,459.
There remains a need for improved methods for the direct flotation of copper from ores containing the sulfides of copper, lead, zinc and other minerals and, in particular, for effecting a primary selective flotation of copper by direct treatment of such ores rather than by the initial formation of a bulk copper-lead concentrate.